Joined Body and Method for Manufacturing Joined Body

This application is a continuation application of PCT/JP2023/046528 filed on Dec. 25.2023, which claims the benefit of priority of Japanese Patent Application No. 2023-011415, filed on Jan. 27, 2023, the entire contents of which are incorporated herein by reference.

The present invention relates to a joined body, and a method for manufacturing a joined body.

As an elastic wave device having a hollow structure, a device is known in which SiOis provided as a dielectric film between a support substrate such as a silicon substrate and a piezoelectric substrate.

PTL 1 discloses an elastic wave apparatus having a hollow structure. The elastic wave apparatus includes a support substrate having a concave part at the upper surface, a thin film provided on the support substrate, a piezoelectric substrate having a first main surface, and a second main surface opposed to the first main surface with the first main surface side arranged on the thin film, and an IDT electrode provided on the second main surface. A cavity surrounded by the support substrate and at least the thin film of the thin film and the piezoelectric substrate is formed, and the thin film is arranged in the area on the first main surface of the piezoelectric substrate, and bonded with the support substrate via the thin film, and at least a partial area of the area above the cavity.

For forming a hollow structure, for example, the following method is used: a film (sacrificial layer) of a different material from that of the dielectric film is formed in a hollow part, and subsequently, the sacrificial layer is removed by etching from the hole part formed in the support substrate or the piezoelectric substrate.

At this step, a small difference in etching rate between the dielectric film and the sacrificial layer causes a concern that not only the sacrificial layer but also the dielectric film may be etched. As a result, a joined body including a desired hollow part may not be able to be obtained.

It is an object of the present invention to provide a joined body including a desired hollow part. Further, it is another object of the present invention to provide a method for manufacturing a joined body, in which the difference in etching rate from the sacrificial layer is large, and by which the sacrificial layer can be selectively removed during etching.

In order to solve the foregoing problem, the present invention provides a joined body including a piezoelectric layer including a piezoelectric material, a dielectric film arranged under the piezoelectric layer, a support substrate joined with the piezoelectric layer via the dielectric film, and a sacrificial layer provided between the support substrate and the piezoelectric layer, and capable of including a hollow part formed therein, in which the dielectric film includes SiOas a main component, and has a H content of 0% or more and 1% or less in terms of atomic ratio.

Further, the present invention provides a joined body including a piezoelectric layer including a piezoelectric material, a dielectric film arranged under the piezoelectric layer, a support substrate joined with the piezoelectric layer via the dielectric film, and a hollow part provided between the support substate and the piezoelectric layer, in which the dielectric film includes SiOas a main component, and has a H content of 0% or more and 1% or less in terms of atomic ratio.

Still further, the present invention provides a method for manufacturing a joined body, the method including a sacrificial layer forming step of forming a sacrificial layer on a piezoelectric substrate, a dielectric film forming step of forming a dielectric film including SiOas a main component, and having a H content of 0% or more and 1% or less in terms of atomic ratio on the piezoelectric substrate and sacrificial layer, a joining step of joining the dielectric film and the support substrate, a film thinning step of thinning the piezoelectric substrate, and obtaining a piezoelectric layer, and a removing step of removing the sacrificial layer, and forming a hollow part between the support substrate and the piezoelectric layer.

Furthermore, the present invention provides a method for manufacturing a joined body, the method including a sacrificial layer forming step of forming a sacrificial layer on a piezoelectric substrate, a dielectric film forming step of forming a dielectric film including SiOas a main component, and having a refractive index of 1.468 or more and 1.471 or less on the piezoelectric substrate and the sacrificial layer, a joining step of joining the dielectric film and the support substrate, a film thinning step of thinning the piezoelectric substrate, and obtaining a piezoelectric layer, and a removing step of removing the sacrificial layer, and forming a hollow part between the support substrate and the piezoelectric layer.

It is possible to provide a joined body including a desired hollow part. Further, it is possible to provide a method for manufacturing a joined body in which the difference in etching rate from the sacrificial layer is large, and by which the sacrificial layer can be selectively removed during etching.

Below, referring to the accompanying drawings, embodiments of the present invention will be described in details.

is a view showing a joined bodyof the present embodiment.

The shown joined bodyhas a structure in which a piezoelectric layer, a dielectric film, and a support substrateare stacked in this order from the upper part in the drawing. Further, a hollow partis provided between the support substrateand the piezoelectric layer

The piezoelectric layeris a layer including a piezoelectric material. The piezoelectric material is selected according to the application in which the joined bodyis used. The piezoelectric materials may include, but are not limited to, for example, LiNbO(LN) and LiTaO(LT). Silicon (Si), gallium arsenide (GaAs), silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), solid solution ceramics (PZT), or the like is appropriately selected.

The dielectric filmis the layer to be arranged under the piezoelectric layer. Although described particularly later, the dielectric filmincludes SiOas the main component. Namely, the dielectric filmcan also be said to be a SiOfilm or a SiOlayer. Further, the dielectric filmhas a H (hydrogen) content of 0% or more and 1% or less in terms of atomic ratio. Still further, for the dielectric filmincluding SiOas the main component, the refractive index of SiOis preferably 1.468 or more and 1.471 or less. A refractive index falling within this range facilitates control of the etching rate to 200 nm/min or less. Incidentally, the measurement of the refractive index of SiOcan be performed by means of, for example, a spectroscopic ellipsometer, and a wavelength of 633 nm can be used.

The support substratewill serve as the support of the whole joined body. Further, the support substrateis joined with the piezoelectric layervia the dielectric film. As the support substrate, a given proper substrate can be used. The support substratemay include a single crystalline body, or may include a polycrystalline body. Alternatively, the support substratemay include a metal.

The material configuring the support substrateis preferably selected from the group consisting of silicon, SiAlON, sapphire, cordierite, mullite, glass, quartz, rock crystal, alumina, SUS, iron nickel alloy (alloy), and brass. Although the thickness of the support substrateis, for example, 0.3 to 1 mm, another given proper thickness than these can be adopted.

The silicon may be single crystal silicon, may be polycrystal silicon, or may be high resistance silicon. Alternatively, the support substratemay be SOI (Silicon on Insulator).

Typically, the SiAlON is ceramics obtained by sintering the mixture of silicon nitride and alumina, and has, for example, a composition represented by SiAlON. Specifically, SiAlON has a composition obtained by mixing alumina in silicon nitride, and w in the formula represents the mixing ratio of alumina. w is preferably 0.5 or more and 4.0 or less.

Typically, the sapphire is a single crystalline body having the composition of AlO, and the alumina is a polycrystalline body having the composition of AlO. Alumina is preferably translucent alumina.

Typically, the cordierite is ceramics having a composition of 2MgO·2AlO·5SiO, and the mullite is ceramics having a composition within the range of 3AlO·2SiOto 2AlO·SiO.

The hollow partis formed at the concave part provided at the dielectric filmin the present embodiment. Hole partsandare formed in the piezoelectric layer, and the hole partsandcommunicate with the hollow part.

The structure of the shown joined bodycan be used as each structure of various devices. Examples of the device may include a high-frequency device, a power semiconductor, a semiconductor laser, a surface acoustic wave filter (SAW (Surface Acoustic Wave) filter), and a thin film piezoelectric MEMS (Micro Electro Mechanical Systems).

Next, a method for manufacturing the joined bodywill be described.

is a flowchart for illustrating the method for manufacturing the joined body. Further,are each a view showing the state corresponding to each step shown in.

First, a piezoelectric substrateis prepared, and a sacrificial layeris formed at the piezoelectric substrate(Step: sacrificial layer forming step) (). The sacrificial layerbecomes the hollow partby being removed by a later step. Accordingly, the sacrificial layeris formed at the site where the hollow partis desired to be formed. The sacrificial layercan be formed as a metal such as Ni, Cu, Al, or Si, an insulation film of SiO, ZnO, PSG (phosphosilicate glass), or the like, an organic film, or the like. The sacrificial layercan be formed by vacuum evaporation, sputtering, CVD, spin coating, or the like.

Further, on the piezoelectric substrateand the sacrificial layer, the dielectric filmincluding SiOas the main component, and having a H content of 0% or more and 1% or less in terms of atomic ratio is formed (Step: dielectric film forming step) (). In this case, the dielectric filmis formed in such a manner as to cover the piezoelectric substrateand the sacrificial layer. The formation method of the dielectric filmwill be described in details later.

Next, the support substrateis prepared, and the dielectric filmand the support substrateare joined (Step: joining step) (). The step is performed by using, for example, the Plasma Activated Bonding (PAB) method in which the joint surface between the dielectric filmand the support substrateis subjected to a surface treatment in vacuum for activation, thereby joining both at ordinary temperatures. Incidentally, when the dielectric filmand the support substrateare joined, a dielectric film (SiO) is deposited on a part of the support substrate, and the partial dielectric film deposited on the support substrate, and the dielectric filmformed on the piezoelectric substratemay be subjected to Plasma Activated Bonding.

Then, the piezoelectric substrateis polished, thereby forming the piezoelectric layer(Step) (.

Incidentally, the following method can also be used. At Step, hydrogen ions or helium ions are injected into the surface of the piezoelectric substrate, and at Step, the site at the depth at which the ions have been injected is set as a separation surface, thereby separating the piezoelectric substrate. In the present embodiment, any method may be adopted. Even when any method is adopted, the Stepcan be grasped as a film thinning step of thinning the piezoelectric substrate, and obtaining the piezoelectric layer

In order to allow the joined bodyto function as a surface acoustic wave filter, an upper electrode and an IDT (Interdigital Transducer) electrode may be formed on the piezoelectric layer. The electrodes are manufactured by using a conductive material such as Al (aluminum). The electrodes can be formed by, for example, the vacuum evaporation lift method.

Further, the sacrificial layeris removed, and the hollow partis formed between the support substrateand the piezoelectric layer(Step: removing step) (). In order to perform this, first, the resist film is patterned by photolithography. Then, an etching gas is allowed to flow thereinto, thereby forming the hole partsand. The hole partsandpenetrate through the piezoelectric layer, and reach the sacrificial layer. Then, an etching gas or an etchant is allowed to flow thereinto via the hole partsand, thereby removing the sacrificial layer. As a result of this, the site where the sacrificial layeris formed becomes the hollow part. Namely, the sacrificial layeris removed by dry etching or wet etching, thereby forming the hollow part.

Further, after the step of, a protective layer including an insulation film can be formed on the piezoelectric layer, the upper electrode, or the IDT electrode. Furthermore, an external terminal may be formed at the upper electrode, or the IDT electrode.

With the steps up to this point,can be grasped as the joined body of the present embodiment.

Next, the formation method of the dielectric filmwill be described in details.

is a view showing a reactive sputtering apparatusto be used for forming the dielectric film. Namely,is an apparatus to be used for performing the Stepof, and the step of.

The shown reactive sputtering apparatusincludes a chamber, a rotative drum type substrate holderto be arranged in the chamber, a targetto be arranged in the reactive sputtering apparatus, a sputtering power supply, a radical oxidation source, and a radical source power supply.

The reactive sputtering apparatusis an apparatus for performing reactive sputtering using silicon (Si) as the target, using an oxygen (O) gas and an argon (Ar) gas. The piezoelectric substrate() including the sacrificial layerformed thereon is arranged at the rotative drum type substrate holder. In this case, while an argon gas is introduced as it is into the chamber, an oxygen gas is previously made into radicals by the radical oxidation source, and is introduced as oxygen radicals into the chamber. Then, silicon configuring the targetis sputtered by the sputtering power supply, and a silicon film is formed on the piezoelectric substrateand the sacrificial layer. This is oxidized by oxygen radicals, resulting in a silicon oxide (SiO) film. As a result of this, it is possible to form the dielectric filmincluding SiOas the main component. Further, a plurality of objects for deposition can be set at the rotative drum type substrate holder. By changing the deposition conditions while rotating the rotative drum type substrate holder, it is possible to form a dielectric filmunder various deposition conditions. The deposition conditions include the flow rate of an argon gas, the flow rate of an oxygen gas, the oxygen radical discharge output, and the sputtering discharge output.

In the present embodiment, the dielectric filmincluding SiOas the main component, and having a H content of 0% or more and 1% or less in terms of atomic ratio is formed. From the viewpoints of making the dielectric filmless likely to be etched, and facilitating selective etching of the sacrificial layer, the H content is preferably 0.1% or more and 1.0% or less, and more preferably 0.2% or more and 0.9% or less. In order to obtain such a dielectric film, for example, at least one of the following (1) and (2) is preferably used as the deposition condition.

As a result of this, it is possible to form the dielectric filmwith a low etching rate. Further, this can be also said that it is possible to form the dielectric filmwith a large difference in etching rate from the sacrificial layer. In consequence, it is possible to provide the joined bodyincluding the hollow partwith a desired size at a desired position. Furthermore, it is possible to provide a method for manufacturing a joined body with a large difference in etching rate from the sacrificial layer, the method being capable of selectively removing the sacrificial layerduring etching.

Using the reactive sputtering apparatusshown in, under the deposition conditions shown in Table 1 below, the dielectric filmincluding SiOwas manufactured. Incidentally, the thickness of the dielectric filmwas set at 500 nm. Incidentally, the case where the discharge output of oxygen radicals is 3000 W, or the case where the flow rate for introducing an argon gas is 400 sccm may be referred to as the standard condition.

The following Table 1 shows the ratio of each parameter when the standard condition is assumed to be 1. Incidentally, the flow rate of an oxygen gas and the sputtering discharge output were set uniform.

As shown in Table 1, the dielectric filmswere formed under 16 different deposition conditions of levels 1 to 16. Out of these, the levels 1 to 4, 11, and 16 satisfy both the deposition conditions of the (1) and (2). Whereas, although the levels 5, 8, 12, 13, and 15 satisfy the deposition condition of the (2), they do not satisfy the deposition condition of the (1). Further, although the levels 6, 7, and 10 satisfy the deposition condition of the (1), they do not satisfy the deposition condition of the (2). Still further, the levels 9 and 14 satisfy neither of the deposition conditions of the (1) and (2).

Buffered hydrofluoric acid was used for etching whose etching rate of the dielectric filmwas evaluated. The thicknesses of the dielectric filmbefore and after etching were calculated using a spectroscopic ellipsometer, and the etching rate was calculated from the difference in film thickness and the etching time. At this step, the case where the etching rate was 200 nm/min or less was rated as success, and the case where the etching rate exceeded 200 nm/min was rated as failure.

Below, the evaluation results will be described.

is a view showing each etching rate of levels 1 to 16.